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Diy decouple subwoofer


dtr20

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Its not the driver causing the problem, its the cabinet.

 

Ridiculous example, but just for fun since weight and friction doesn't matter, I'm curious, if we theoretically made a typical sealed subwoofer box out of an infinitely strong yet insanely light material whose panels could not flex or resonate, drop in an ultra-high excursion driver that fired to the front, fed it about 1.21 jigawatts, then installed the enclosure in such a way that there is little to no friction, such as having a hard plastic bottom then set it in the middle of a freshly Zamboni'ed ice rink, or maybe even donate it to the International Space Station...

 

would it vibrate at all?   :)

Edited by MetropolisLakeOutfitters
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Its not the driver causing the problem, its the cabinet.

 

Ridiculous example, but just for fun since weight and friction doesn't matter, I'm curious, if we theoretically made a typical sealed subwoofer box out of an infinitely strong yet insanely light material whose panels could not flex or resonate, drop in an ultra-high excursion driver that fired to the front, fed it about 1.21 jigawatts, then installed the enclosure in such a way that there is little to no friction, such as having a hard plastic bottom then set it in the middle of a freshly Zamboni'ed ice rink, or maybe even donate it to the International Space Station...

 

would it vibrate at all?   :)

 

 

Ridiculous example on my part and then you spew that trash ?

 

It may be national bourbon day but there is no reason to drink until heavily intoxicated and post here with that nonsense.

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Ridiculous example on my part and then you spew that trash ?

 

It may be national bourbon day but there is no reason to drink until heavily intoxicated and post here with that nonsense.

 

 

Chill out a  little, it's obviously a ridiculous example on my part.  I was trying to include a disclaimer about it.  Didn't work I suppose.  

 

Still curious though, would this vibrate?  Just wondering if you can grasp basic concepts of physics.  

Edited by MetropolisLakeOutfitters
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This thread took a turn. Jason, are you saying that the subs you built are so strong, that when you play loud deep bass, there are no vibrations that transfer from the cabinet to the floor through the feet?

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This thread took a turn. Jason, are you saying that the subs you built are so strong, that when you play loud deep bass, there are no vibrations that transfer from the cabinet to the floor through the feet?

 

No.

 

What i am saying is heavy cabinet panels resonating is normally the cause of a walking cabinet.

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I think of coupling as the relationship of the sound waves to the floor, wall or corner rather than vibrations from the enclosure to the floor. The way you decouple a speaker or sub from the floor or wall is put distance between them. For bass this is usually a bad idea. I understand that what you want it to provide dampening between the cabinet and the floor. That way, the vibrations of the sub don't transfer into the floor causing distortion by making the floor a sort of loudspeaker itself made of very poor materials. If you do this and are still coupled to the floor (close to it) or the corner, then the floor or walls act as reflectors and in corners even as horns. 

 

As for subs that don't walk or vibrate, I expect a sub with a down firing driver would tend to vibrate less. Add to that the added materials, the increased efficiency meaning less excursion, the lighter cones and physical size of making a horn loaded sub, there would be little perceptible vibration. I think that's where Jason is coming from. Sorry if I'm off base. 

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Sub walking on the floor is one thing and decoupling is another.  A rubber mat from Homedepot can help stop walking and some floor vibrations.  Technically, you can't stop a sub from going thru walls, floor, upstairs, ect.  This is caused by the long bass waves from the sub. 

 

Subs can be used on risers to help clean up the sound.  This will effect the floor bounce and can change vertical modal behavior.  As with all good things, the down side is the riser needs to be 2 ft. high and also changing the vertical modal interaction may not be good.  I use mini risers for most of my subs because it makes them easy to move.  I think they sound better but, can't back it up by any room measurements.  I've tired, he, he.

Edited by derrickdj1
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As for subs that don't walk or vibrate, I expect a sub with a down firing driver would tend to vibrate less. Add to that the added materials, the increased efficiency meaning less excursion, the lighter cones and physical size of making a horn loaded sub, there would be little perceptible vibration. I think that's where Jason is coming from. Sorry if I'm off base. 

 

Never noticed any difference in the amount of vibration between vertical or horizontal firing designs though obviously there is a difference and my guess is that horizontal would be more susceptible to scooting across the floor.

 

Never mentioned anything about horns here, just stating what i have experienced.

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As for subs that don't walk or vibrate, I expect a sub with a down firing driver would tend to vibrate less.

 

Depends on the floor.  Scrappy had one of those SVS down firing cylinder subs in his living room, which is fully suspended over the downstairs area.  I thought he was exaggerating but I visited and it was ridiculous.  On any big sub hit that was pretty low, the energy transferred to the floor which flexed it, A LOT.  This wasn't just a small vibration that tickled  No, it literally felt like the floor was going to cave in.  First time I felt it I was standing up and had an innate reaction where my knees buckled and I was looking for something to grab on to.  Yes it is that extreme.  

Edited by MetropolisLakeOutfitters
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As for subs that don't walk or vibrate, I expect a sub with a down firing driver would tend to vibrate less. Add to that the added materials, the increased efficiency meaning less excursion, the lighter cones and physical size of making a horn loaded sub, there would be little perceptible vibration. I think that's where Jason is coming from. Sorry if I'm off base. 

 

Never noticed any difference in the amount of vibration between vertical or horizontal firing designs though obviously there is a difference and my guess is that horizontal would be more susceptible to scooting across the floor.

 

Never mentioned anything about horns here, just stating what i have experienced.

 

I got to thinking about it, and every sub I have ever had has been on carpet except the KPT-684's I have now. The 684's have rubber feet and weigh a ton. On top of that, they are heavy with rubber feet. Also, I wonder that since they are ported, the jet of air coming out of the ports offsets some of the excursion of the cone.

 

I kinda think of it like an umbrella. If you pull an umbrella there is air resistance, and you can pull yourself forward with it. There is less resistance if you push the umbrella, but there is still some. This is like a woofer cone. Although there is mass moving forward and backward, it's nominal compared to the air pressure. The same holds true with the port, except I compare that to a jet. Maybe calculations would show the air resistance of the cone matches that of the port after the pressure starts to equalize, I don't know. Either way, it would seem a sealed or a ported with the port on the back would be worse than one with a front port in a vertical driver oriented sub.

 

It is a good topic for discussion, and perhaps might shed some light on why all the designs you have had experience with cause no perceivable vibrations.

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As for subs that don't walk or vibrate, I expect a sub with a down firing driver would tend to vibrate less.

 

Depends on the floor.  Scrappy had one of those SVS down firing cylinder subs in his living room, which is fully suspended over the downstairs area.  I thought he was exaggerating but I visited and it was ridiculous.  On any big sub hit that was pretty low, the energy transferred to the floor which flexed it, A LOT.  This wasn't just a small vibration that tickled. No, it literally felt like the floor was going to cave in.  First time I felt it I was standing up and had an innate reaction where my knees buckled and I was looking for something to grab on to.  Yes it is that extreme.  

 

That's a good point. I was commenting on the term decouple earlier, and this would be a great example of how I may be partially wrong. The floor does indeed become a speaker itself when coupled whether by physical contact or by sound pressure from waves. I suppose the term uncoupling by dampening and uncoupling by distance are two ways of looking at it. Either way, it seems like the acoustic properties of the materials you are coupled to would make a difference if I am guessing right. I wonder if there is a perceivable difference in drywall, hardwood, aluminum, glass, etc...

Edited by mustang guy
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I got to thinking about it, and every sub I have ever had has been on carpet except the KPT-684's I have now. The 684's have rubber feet and weigh a ton. On top of that, they are heavy with rubber feet. Also, I wonder that since they are ported, the jet of air coming out of the ports offsets some of the excursion of the cone.

 

I kinda think of it like an umbrella. If you pull an umbrella there is air resistance, and you can pull yourself forward with it. There is less resistance if you push the umbrella, but there is still some. This is like a woofer cone. Although there is mass moving forward and backward, it's nominal compared to the air pressure. The same holds true with the port, except I compare that to a jet. Maybe calculations would show the air resistance of the cone matches that of the port after the pressure starts to equalize, I don't know. Either way, it would seem a sealed or a ported with the port on the back would be worse than one with a front port in a vertical driver oriented sub.

 

It is a good topic for discussion, and perhaps might shed some light on why all the designs you have had experience with cause no perceivable vibrations.

Assuming the box is braced/built properly, a ported one should be much less of an issue in this regard than a sealed one, not because it has a jet pack though, but because near the tuning frequency of the port, the backpressure from the port is so high that the woofer barely moves comparatively. You're looking at internal pressures that are nearly twice that of sealed boxes due to the backpressure. A cone in a ported box is basically cracking a whip on the air in the port, which creates high pressure while the air comes in, and a vacuum when it goes out. Most people think that the air shooting out is the same amount of air that is displaced by the cone, but it's not, it's higher.

Edited by MetropolisLakeOutfitters
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To explain my previous comments with a major geek out session, watch the video below.  Notice how the sub compresses the padding on the stool a little bit.  Why is this?  When the cone moves out, energy is exerted on everything else, which makes it move in a free-air or at least low friction environment.  It's the same thing as rifle recoil.  The cone can't be shot forward without the basket/magnet experiencing recoil.  

 

The only way to minimize this is to add mass.  The most basic physics formula in the world is F = MA (Newton's second law of motion), or force = mass times acceleration.  You can also flip it around and see that acceleration = force divided by mass.  In other words, if force stays the same, when mass goes up, acceleration goes down.  Adding an enclosure would add mass, but in an environment with no friction, it would be the equivalent of a "limit" in calculus... you're never going to totally get rid of it.  So a sub in an enclosure is still going to have this effect, just not as bad.  The other way to minimize acceleration is to reduce force.  Horns and vented subs where the cone isn't moving as much would be an example.  

 

So yes, in this regard, enclosure weight matters.  More weight slows down the acceleration of the box that the sub is attached to, and if you say it's not moving in the first place, it's because this extra weight is also exerting more friction on the floor, and the force on the box exerted by the sub is simply not sufficient to overcome this friction.  

 

Just think though, this video is just a single 10" sub.  Fs is only like 42 hz plus like I said, it's only a single 10.  Imagine now that you have two 18's with a low Fs instead.  The cone area alone is 7.5 times this amount, but the overall moving mass is probably higher.  That is A LOT of energy exerted by the subs.  Imagine the force that is compressing the pad on this stool being like 10 times this amount, moving this much and this fast, with 3 pounds being thrown back and forth in both directions.  It's not insignificant.  Just think, for a 20 hz test tone, that's potentially 3 pounds moving 2" in one direction, 2" in the other direction, all in 0.05 seconds.  You have to counteract that somehow.  

 

My point is that when you talk about decoupling a powerful sealed sub that is moving A LOT, you're basically minimizing this friction, you're potentially letting the box move more like it was in free-air.  You can see this effect if you build a lightweight box that has a good amount of surface area on the bottom, install a powerful home theater driver, and set the box on some thick shag carpet.  The entire enclosure will move a small amount no matter how well you brace it.  By decoupling, you are doing this on purpose.  In my opinion, it's not a good thing.  

 

 

Edited by MetropolisLakeOutfitters
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The larger driver will use a larger cabinet making any differences minimal at best.

 

Larger cabinets means beefier bracing as well adding more weight.

 

Build at least a few dozen cabinets and get back to the thread to post your results.

 

Pretty sure dam near everybody here has seen a woofer move before, why post that ?

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The larger driver will use a larger cabinet making any differences minimal at best.

 

Larger cabinets means beefier bracing as well adding more weight.

Weight is a non issue.

 

Throwing weight on a vibrating sub is band-aid fix.

Hmmm...

Pretty sure dam near everybody here has seen a woofer move before, why post that ?

Because this illustrates the force that acts in the opposite direction as the cone movement.

Edited by MetropolisLakeOutfitters
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